We have recently expanded our efforts to chromosomally map genes in the laboratory mouse. Such studies have received increased interest through the Human Genome Initiative, which views the mouse as a unique model system. Our studies, traditionally based on the analysis of somatic cell hybrids to assign genes to chromosomes, have been expanded to include Southern blot analysis of DNAs from an interspecies cross. These studies have resulted in the chromosomal mapping of genes encoding zona pellucida proteins and enzymes, genes involved in drug metabolism, brain-specific genes, and numerous genes involved in visual transduction, including a cDNA which may be responsible for retinal degeneration, an inherited disorder.